在檔案裡設定一個點選方法已進行點選下載：

download.setOnClickListener(new View.OnClickListener() {
    @Override
public void onClick(View v) {
        String filePath = imageInfo.get(currentItem).getBigImageUrl();
ImgDonwload.donwloadImg(ImageActivity.this,filePath);
}
});

下面是ImgDonwload.java圖片下載工具類：

package com.vimi8.app.utils.imagesUtils;
 
import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
 
import android.widget.Toast;
import java.io.BufferedOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.UUID;
/**
 * Created by vimi8 on 2017/6/9.
 
 */
public class ImgDonwload {

    private static String filePath;
    private static Bitmap mBitmap;
    private static String mFileName="為米老鄉";
    private static String mSaveMessage;
    private final static String TAG = "ImageActivity";
    private static Context context;
    private static ProgressDialog mSaveDialog = null;
    public static void donwloadImg(Context contexts,String filePaths){
        context = contexts;
filePath = filePaths;
mSaveDialog = ProgressDialog.show(context, "儲存圖片", "圖片正在儲存中，請稍等...", true);
        new Thread(saveFileRunnable).start();
}

    private static Runnable saveFileRunnable = new Runnable(){
        @Override
public void run() {
            try {
                byte[] data = getImage(filePath);
                if(data!=null){
                    mBitmap = BitmapFactory.decodeByteArray(data, 0, data.length);// bitmap
}else{
                    Toast.makeText(context, "Image error!", Toast.LENGTH_LONG).show();
}



                saveFile(mBitmap, mFileName);
mSaveMessage = "圖片儲存成功！";
} catch (IOException e) {
                mSaveMessage = "圖片儲存失敗！";
e.printStackTrace();
} catch (Exception e) {
                e.printStackTrace();
}
            messageHandler.sendMessage(messageHandler.obtainMessage());
}

    };
    private static Handler messageHandler = new Handler() {
        @Override
public void handleMessage(Message msg) {
            mSaveDialog.dismiss();
Log.d(TAG, mSaveMessage);
Toast.makeText(context, mSaveMessage, Toast.LENGTH_SHORT).show();
}
    };
/**
     * Get image from newwork
     * @param path The path of image
     * @return byte[]
     * @throws Exception
     */
public static byte[] getImage(String path) throws Exception{
        URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setConnectTimeout(5 * 1000);
conn.setRequestMethod("GET");
InputStream inStream = conn.getInputStream();
        if(conn.getResponseCode() == HttpURLConnection.HTTP_OK){
            return readStream(inStream);
}
        return null;
}

    /**
     * Get data from stream
     * @param inStream
* @return byte[]
     * @throws Exception
     */
public static byte[] readStream(InputStream inStream) throws Exception{
        ByteArrayOutputStream outStream = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int len = 0;
        while( (len=inStream.read(buffer)) != -1){
            outStream.write(buffer, 0, len);
}
        outStream.close();
inStream.close();
        return outStream.toByteArray();
}


    /**
     * 儲存檔案
     * @param bm
* @param fileName
* @throws IOException
     */
public static void saveFile(Bitmap bm, String fileName) throws IOException {
        File dirFile = new File(Environment.getExternalStorageDirectory().getPath());
        if(!dirFile.exists()){
            dirFile.mkdir();
}
        fileName = UUID.randomUUID().toString()+".jpg";
File jia=new File(Environment.getExternalStorageDirectory().getPath() +"/DCIM/VIMI8");
        if(!jia.exists()){   //判斷資料夾是否存在，不存在則建立
jia.mkdirs();
}
        File myCaptureFile = new File(jia +"/"+ fileName);
BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(myCaptureFile));
bm.compress(Bitmap.CompressFormat.JPEG, 80, bos);
bos.flush();
bos.close();
//把圖片儲存後宣告這個廣播事件通知系統相簿有新圖片到來
Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
Uri uri = Uri.fromFile(myCaptureFile);
intent.setData(uri);
context.sendBroadcast(intent);
}
}

以上是取得的是byte陣列, 從byte陣列生成bitmap

以下是取得的是InputStream，直接從InputStream生成bitmap

package com.vimi8.app.utils.imagesUtils;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.widget.Toast;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.UUID;
/**
 * Created by vimi8 on 2017/6/9.
 */
public class ImgDonwloads {

    private static String filePath;
    private static Bitmap mBitmap;
    private static String mFileName="為米老鄉";
    private static String mSaveMessage;
    private final static String TAG = "ImageActivity";
    private static Context context;
    private static ProgressDialog mSaveDialog = null;
    public static void donwloadImg(Context contexts,String filePaths){
        context = contexts;
filePath = filePaths;
mSaveDialog = ProgressDialog.show(context, "儲存圖片", "圖片正在儲存中，請稍等...", true);
        new Thread(saveFileRunnable).start();
}

    private static Runnable saveFileRunnable = new Runnable(){
        @Override
public void run() {
            try {
                mBitmap = BitmapFactory.decodeStream(getImageStream(filePath));
saveFile(mBitmap, mFileName);
mSaveMessage = "圖片儲存成功！";
} catch (IOException e) {
                mSaveMessage = "圖片儲存失敗！";
e.printStackTrace();
} catch (Exception e) {
                e.printStackTrace();
}
            messageHandler.sendMessage(messageHandler.obtainMessage());
}

    };
    private static Handler messageHandler = new Handler() {
        @Override
public void handleMessage(Message msg) {
            mSaveDialog.dismiss();
Log.d(TAG, mSaveMessage);
Toast.makeText(context, mSaveMessage, Toast.LENGTH_SHORT).show();
}
    };
/**
     * Get image from newwork
     * @param path The path of image
     * @return InputStream
     * @throws Exception
     */
public static InputStream getImageStream(String path) throws Exception{
        URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setConnectTimeout(5 * 1000);
conn.setRequestMethod("GET");
        if(conn.getResponseCode() == HttpURLConnection.HTTP_OK){
            return conn.getInputStream();
}
        return null;
}





    /**
     * 儲存檔案
     * @param bm
* @param fileName
* @throws IOException
     */
public static void saveFile(Bitmap bm, String fileName) throws IOException {
        File dirFile = new File(Environment.getExternalStorageDirectory().getPath());
        if(!dirFile.exists()){
            dirFile.mkdir();
}
        fileName = UUID.randomUUID().toString()+".jpg";
File myCaptureFile = new File(Environment.getExternalStorageDirectory().getPath() +"/DCIM/Camera/"+ fileName);
BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(myCaptureFile));
bm.compress(Bitmap.CompressFormat.JPEG, 80, bos);
bos.flush();
bos.close();
//把圖片儲存後宣告這個廣播事件通知系統相簿有新圖片到來
Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
Uri uri = Uri.fromFile(myCaptureFile);
intent.setData(uri);
context.sendBroadcast(intent);
}
}